Dimensional gages are used to confirm the shape of a part or workpiece. Examples of workpieces often measured with dimensional gages include brake rotors, drums, flywheels and similar precision turned parts. Dimensional gaging helps to ensure that feature size and shape meet drawing requirements and are suitable for use as a component of a larger assembly. Typical dimensional gaging criteria usually specify that external features be measured with respect to specific datums, such as, for example a mounting surface and a bore diameter. Lateral runout for a disc brake rotor or circular runout for a brake drum are normally specified this way and are critical to workpiece performance.
Typically the mounting surface has been measured dynamically, i.e., during rotation of the part. The bore diameter is measured statically—without movement of the part. With known dimensional gages, two separate stations have been required as it has not been simultaneously possible to locate and to measure both of these critical dimensions. Typically a single station would dynamically measure a mounting surface, but could not measure the bore diameter because the bore was occupied by a collet or other centering and clamping part. Therefore a second gaging station was required to measure bore diameter. A two station gaging operation takes up space and is relatively expensive. Moreover additional time is required for transfer of the part. It would be desirable to provide a single station dimensional gage which can make both static measurements and dynamic measurements of a workpiece.